1. Field of the Invention
This invention relates to digital displays, more particularly to digital signal processing of the video signal in such displays.
2. Background of the Invention
Most televisions in use today utilize a cathode-ray tube (CRT) display. Because of this standard broadcast signals have been optimized for this format. Digital television, namely those using binary (ON/OFF) spatial light modulators, such as liquid crystal displays (LCD) or deformable mirror device (DMD) displays, have a different input signal requirement for their displays, which can result in a much better picture.
The relationship between displayed brightness and the input voltage is not linear. It is exponential. The output brightness varies according to the following formula: EQU B=V.sup..gamma.
where B is brightness, V is the input voltage, and the exponent ".gamma.", is referred to as gamma. Depending on the CRT used, gamma varies from 2.2 to 3.0. This non-linearity has the effect of compressing the black or low-end portion of the signal, causing low contrast in the low-light areas.
To correct for this non-linearity in standard, CRT based systems, an inverse function: EQU V.sub.out =V.sub.input.sup.1/2.5
is added by the broadcaster sending the signal. This allows the displayed picture to be approximately linear.
In the move to digitized television, a problem arises. Television using spatial light modulators may not need this correction, and it can even interfere with the quality of display on such a television. Some digital systems have a direct linear relationship between brightness and input voltage. The problem is eliminating or nullifying the gamma correction added by the broadcaster in the television system. This allows for compatibility between CRT-based and digital televisions and any standard format. Use of such a nullification regardless of any gamma applied or not applied may also have an improving effect upon the picture displayed.